Sunan Abi Dawud 4091
سنن أبي داود#4091SahihNarrated 'Abd Allah (b. Mas'ud): The Messenger of Allah (ﷺ) as saying: He who has in his heart as much pride as much pride as grain of mustard-seed will not enter paradise. And he who has in his heart as much faith as grain of mustard-seed will not enter Hell. Abu Dawud said: Al-Qasmali has transmitted it from Al-A'mash in a similar way
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Zubair Ali ZaiSahih Muslim (91)
In-book reference: 34:72